Peter Blokker

BIOSYNTHETIC EFFECTS ON THE STABLE CARBON ISOTOPIC COMPOSITIONS OF ALGAL LIPIDS : IMPLICATIONS FOR DECIPHERING THE CARBON ISOTOPIC BIOMARKER RECORD

Thirteen species of algae covering an extensive range of classes were cultured and stable carbon isotopic compositions of their lipids were analysed in order to assess carbon isotopic fractionation effects during their biosynthesis. The fatty acids were found to have similar stable carbon isotopic compositions to each other in all the algae with the exceptions of the C28 fatty acid in Scenedesmus communis and the polyunsaturated fatty acids in Ampidinium sp. and Gymnodinium simplex which are 3.5‰ more depleted in 13C and up to 8‰ more enriched in 13C, compared to the C16 fatty acid, respectively. Phytol is consistently enriched in 13C by 2–5‰ compared with the C16 fatty acid in all algae. The sterols are, however, enriched in 13C by 0–8‰ compared to the C16 fatty acid, possibly due to a different pool of isopentenyl diphosphate in the cytosol. These large ranges in carbon isotopic compositions of compounds biosynthesized by the same eukaryotes can significantly complicate the interpretation of δ13C values of sedimentary biomarkers.

Chemical structure of algaenans from the fresh water algae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum

Abstract The cell walls of the fresh water green microalgae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum are composed of highly resistant, non-hydrolyzable aliphatic biopolymers as revealed by 13C-NMR, FTIR and thermal and chemical degradations. The biopolymers are composed of long-chain even-carbon-numbered ω9-unsaturated ω-hydroxy fatty acid monomers varying in chain length from 30 to 34 carbon atoms. These monomers are intermolecularly ester linked to form linear chains in which the unsaturations act as the starting position of ether cross-linking. S. communis biosynthesises a more densely cross-linked algaenan than T. minimum and P. boryanum. The monomers of T. minimum have, on average, larger chain lengths than those of P. boryanum and S. communis. The polyether nature of these algaenans makes them highly resistant against degradation, so that they are selectively preserved in the sedimentary record. Therefore, these algaenans probably are important precursors for Type I kerogens.

Resistant macromolecules of extant and fossil microalgae

The occurrence and composition of macromolecular resistant walls of microalgae and their fossil macromolecular counterparts are reviewed. To date, several algal groups have been identified to produce fossilizable biomacromolecules. Only two biosynthetic pathways seem to be responsible for this, of which the acetate/malate pathway used by Chlorophyta, Eustigmatophyta and Dinophyta is considered to lead to a series of closely related resistant biomacromolecules, called algaenans. Algaenans consist of a network of predominantly linear carbon chains. A different, as yet unidentified, pathway is used by the Dinophyta to produce the aromatic walls of their cysts. The poly‐ketide or acetogenic pathway may have been responsible for resorcinol‐based algae or bacteria‐derived microfossils of the acritarch Gloeocapsamorpha prisca, either through synthesis of the biomacromolecule or through a third pathway, the post‐mortem polymerization of its resorcinol lipids. The postmortem polymerization of lipids also appears to be responsible for the formation of fatty acid‐based macromolecules in Eocene dinoflagellate‐shaped remains from Pakistan. Finally, there is a clear need for elucidating the chemical differences between the biomacromolecules produced by the algae and their fossil analogs in the sediments. This notably applies to the release and condensation of aliphatic and aromatic moieties both at normal and at elevated temperature and pressure conditions.

UV-B Absorbance and UV-B absorbing compounds (para-coumaric acid) in pollen and sporopollenin: the perspective to track historic UV-B levels.

UV-B absorbance and UV-B absorbing compounds (UACs) of the pollen of Vicia faba, Betula pendula, Helleborus foetidus and Pinus sylvestris were studied. Sequential extraction demonstrated considerable UV-B absorbance both in the soluble (acid methanol) and insoluble sporopollenin (acetolysis resistant residue) fractions of UACs, while the wall-bound fraction of UACs was small. The UV-B absorbance of the soluble and sporopollenin fraction of pollen of Vicia faba plants exposed to enhanced UV-B (10 kJ m(-2) day(-1) UV-B(BE)) was higher than that of plants that received 0 kJ m(-2) day(-1) UV-B(BB). Pyrolysis gas chromatography-mass spectrometry (py-GC-MS) analysis of pollen demonstrated that p-coumaric acid and ferulic acid formed part of the sporopollenin fraction of the pollen. The amount of these aromatic monomers in the sporopollenin of Vicia faba appeared to increase in response to enhanced UV-B (10 kJ m(-2) day(-1) UV-B(BE)). The detection limit of pyGC-MS was sufficiently low to quantify these phenolic acids in ten pollen grains of Betula and Pinus. The experimental data presented provide evidence for the possibility that polyphenolic compounds in pollen of plants are indicators of solar UV-B and may be applied as a new proxy for the reconstruction of historic variation in solar UV-B levels.

Archaeal remains dominate marine organic matter from the early Albian oceanic anoxic event 1b

Abstract The sources for both soluble and insoluble organic matter of the early Albian (∼112 Myr) oceanic anoxic event (OAE) 1b black shales of the Ocean Drilling Program (ODP) site 1049C (North Atlantic Ocean off the coast of Florida) and the Ravel section of the Southeast France Basin (SEFB) were determined using optical, chemical, stable carbon and nitrogen isotopic analyses. Archaea-derived isoprenoidal tetraether membrane lipids and free and macromolecularly bound isoprenoid alkanes are abundant in these black shales. More specifically, the presence of certain ether lipids (bi/tricyclic biphytane tetraethers) indicates an important contribution of representatives of marine planktonic archaea. The large difference (up to 12‰) in 13C/12C ratios between algal biomarkers and the much more abundant planktonic archaea-derived biomarkers indicates that the latter were living chemoautotrophically. This offset in 13C/12C ratios was used to estimate that up to ∼40% of the organic matter of the SEFB and up to ∼80% of the organic matter of ODP site 1049C preserved in the black shales is derived from archaea. Furthermore, it is shown that, even though there are apparent similarities (high organic carbon (OC) content, distinct lamination, 13C-enrichment of OC) between the black shales of OAE1b and the Cenomanian/Turonian (∼94 Myr) OAE, the origin of the organic matter (archaeal versus phytoplanktonic) and causes for 13C-enrichment of OC are completely different.

A comparative study of fossil- and extant algaenans using ruthenium tetroxide degradation

In this study the chemical structure of algaenans isolated from the freshwater algae Tetraedron minimum, Pediastrum boryanum and Botryococcus braunii are compared with their fossil counterparts by means of RuO4 oxidation. The results show that the algaenans investigated are preserved in sediments with only minor structural alterations. However, product mixtures from RuO4 degradation of the fossil algaenans exhibit a broader distribution of oxidation products than freshly isolated algaenans indicating that the fossil biopolymers contain a greater proportion of ether cross-links, which maybe an effect of diagenetic alteration or different algal strains. Despite these differences, fossil algaenans can still be recognised chemically on the basis of the specific RuO4 oxidation products, even after 50 Ma of sediment burial.

Anaerobic biodegradation of lipids of the marine microalga Nannochloropsis salina

In order to determine the susceptibility to anaerobic biodegradation of the different lipid biomarkers present in a marine microalga containing algaenan, portions of one large batch of cultured Nannochloropsis salina (Eustigmatophyceae) were incubated in anoxic sediment slurries for various times. After 442 days, all lipids studied [mono-, di-, and tri-unsaturated hydrocarbons, long-chain unsaturated alcohols and alkyl diols, phytol, sterols, saturated and (poly)unsaturated fatty acids] showed a significant decrease in concentration, which was accompanied by a strong production of sulfide and methane. However, the studied compounds showed a wide range of reactivity and different patterns and extent of degradation. Polyunsaturated fatty acids, phytol and triunsaturated hydrocarbons were the most labile compounds and showed initially rapid degradation rates, followed by a substantial reduction in degradation rate during the later stages of incubation. Long-chain alkyl diols and unsaturated alkenols, known to constitute the building blocks of the algaenan of N. salina, showed fluctuating concentrations with time clearly indicating their release from bound fractions in parallel with their degradation. Other lipids showed a continuous concentration decrease until the end of the incubation, with alkadienes and sterols being the most resistant compounds encountered. Besides providing an extended sequence of reactivity for lipids under anoxic conditions, the results demonstrate that the presence of resistant algaenan in the outer cell wall of microalgae does not protect the other lipids of the cell from anaerobic microbial degradation.

Molecular structure of the resistant biopolymer in zygospore cell walls of Chlamydomonas monoica

Abstract. The unicellular green alga Chlamydomonas monoica Strehlow is known to produce zygospores with a cell wall that is resistant against microbial and chemical attack. This resistance is thought to be due to the presence of a sporopollenin-like material. However, the resistant nature of sporopollenin-like materials seriously hampers their structural analysis. With complementary techniques such as 13C-nuclear magnetic resonance spectroscopy, Curie-point pyrolysis-gas chromatography/mass spectroscopy and RuO4 chemical degradation, the chemical composition of resistant biopolymer in the isolated cell walls of C. monoica zygospores was determined. This material is composed of C22–C30 linear alcohols and carboxylic acids, intermolecularly linked via ester and ether-linkages similar to the resistant aliphatic biopolymers encountered in the walls of the vegetative cells of the algae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum.

The chemical structure of Gloeocapsomorpha prisca microfossils: implications for their origin

Abstract Two Estonian Kukersites (Ordovician) and two samples from the Guttenberg Member (Ordovician) of the Decorah formation (North America) containing botryoidal aggregates of Gloeocapsomorpha prisca were investigated by RuO4 chemical degradation, FTIR, and flash pyrolysis-GC/MS to obtain information about the polymeric structure of these microfossils. The products formed upon oxidation by RuO4 were analysed by GC/MS and revealed the presence of a wide range of carboxyl and/or carbonyl moiety containing compounds with carbon skeletons ranging from C5 to C20. The Estonian Kukersites reveal the presence of a characteristic set of mono-, di-, and tricarboxylic acids. These compounds suggest that the Estonian Kukersites are composed of a polymer consisting of mainly C21 and C23 n-alkenyl resorcinol building blocks. Similarly, although the tricarboxylic acids are not present, the RuO4 degradation product mixtures of the Guttenberg Member samples, suggest a poly(n-alkyl resorcinol) structure. The higher thermal maturity is most likely responsible for the different chemistry and morphology of the G. prisca microfossils in these samples. Because compounds like n-alkenyl resorcinols are known to polymerise under oxygenated conditions even in an aqueous environment, it is not per se necessary that these microfossils are composed of a selectively preserved biopolymeric cell wall. It is also possible that G. prisca microfossils are composed of a cell wall or sheath component that polymerised during senescence or diagenesis of the organism.

Structural biomacromolecules in plants : what can be learnt from the fossil record?

Publisher Summary This chapter describes the chemical methods that provide detailed molecular insight into the chemical composition of both extant and fossil resistant (bio)macromolecules. Numerous chemical extraction methods exist to obtain the most resistant organic molecules in plant remains. The various chemical methods that are used to study the resistant biomacromolecules can be subdivided into nondestructive and destructive techniques. Nondestructive techniques includes solid state 13C NMR and FTIR. The destructive methods include pyrolysis and chemolysis. The chapter discusses the macromolecular composition of outer coverings of modern and fossil plants, including algal cell walls, spore and pollen walls, and cuticular tissues in terms of their chemical similarities and differences and in relation to the physiological adaptations and evolution of land plants. The resistant molecules in cuticles and spore and pollen walls (sporopollenin) are all based on even carbon numbered long-chain aliphatic chemical building blocks, providing sufficient hydrophobicity to reduce water loss. These aliphatic moieties are largely similar to those present in the resistant walls of algae (algaenan) from which the land plants may have evolved. Apart from the aliphatic materials, sporopollenin and, to some degree, cutin and cutan from both modern and fossil examples also reveal the presence of cinnamic acids, which probably are responses to the enhanced levels of ultraviolet radiation on land. Finally, the chapter evaluates the chemical composition of water-conduction tissues of modern and fossil land plants in terms of their physiology but with specific emphasis on the biomacromolecule lignin.